The undercover officer is said to have gathered personal details about Doreen Lawrence, Stephen’s mother.
Photograph: Nick Ansell/PA

An undercover police officer accused of spying on the family of the murdered teenager Stephen Lawrence has been officially identified as David Hagan.

He is a key figure in the controversy over the use of police spies to gather information about the Lawrence family while they were trying to persuade the police to properly investigate their son’s racist murder.

His fake identity was published on Tuesday by the judge-led public inquiry examining the conduct of undercover officers who were sent to infiltrate political groups. He lost a legal argument to keep his identity concealed.

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Hagan has previously been labelled “a spy in the Lawrence family camp” by an official report, which said he had gathered personal details about Doreen and Neville Lawrence, the parents of the murdered teenager, including about the breakdown of their marriage.

He passed “fascinating and valuable” information about them to his Scotland Yard superiors, according to the report, which did not name him and referred to him by the cipher N81.

His superiors allegedly exploited the information to help defend themselves against accusations that the police had bungled the investigation into Stephen’s murder, 25 years ago this month.

May set up the public inquiry into the undercover infiltration of political groups after the revelations in 2014. It also followed a series of disclosures about the conduct of undercover officers, including how some had deceived women into long-term relationships.

Sir John Mitting, the judge leading the inquiry, has said one of the crucial issues will be to determine the involvement of Hagan and his colleagues in the monitoring of the Lawrences during the family’s quest to establish who killed their son.

Brooks said on Tuesday: “At last the speculation is over and I can try and piece together what parts of my life Hagan intruded on. Which bits of my private life did he snoop on?”

The Lawrences have repeatedly called for the inquiry to uncover the full truth of how they were spied on. They complain, however, along with many others subjected to surveillance, that Mitting has unfairly allowed the police to cover up their misconduct.

Hagan was a member of a covert unit, the Special Demonstration Squad, which infiltrated political groups, going undercover between 1996 and 2001 when he pretended to be a leftwing activist.

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The inquiry confirmed that he had infiltrated an anti-racist group known as the Movement for Justice, which supported the Lawrences’ campaign. He infiltrated other groups including the Socialist Workers party and the anarchist organisation Class War.

Some details of Hagan’s deployment were made public in 2014 after May had asked a QC, Mark Ellison, to investigate.

In his report, Ellison described how Hagan had a meeting in 1998 with a senior Metropolitan police officer who was then involved in drawing up the defence of its conduct during the murder investigation.

According to Ellison, opening up this channel of communication was “wrongheaded and inappropriate” and could be seen as giving the Met a “secret advantage” over the family.

Hagan has said he has mental health problems as a result of his deployment and fears his real identity could be exposed. He had argued that his real name and the fake identity he used while undercover should be kept secret.

Mitting, however, ruled that his fake identity should be published to enable the Lawrence family and other campaigners to give evidence about him on a critical issue.

The inquiry has been delayed because many of the undercover officers have submitted legal applications to keep their identities secret.